586 research outputs found
Tight asymptotics of clique-chromatic numbers of dense random graphs
The clique chromatic number of a graph is the minimum number of colors
required to assign to its vertex set so that no inclusion maximal clique is
monochromatic. McDiarmid, Mitsche and Pra\l at proved that the clique chromatic
number of the binomial random graph is at most
with high probability. Alon and
Krivelevich showed that it is greater than with high
probability and suggested that the right constant in front of the logarithm is
We prove their conjecture and, beyond that, obtain a tight
concentration result: whp $\chi_c\left(G\left(n,1/2\right)\right) =
\frac{1}{2}\log_2 n - \Theta\left(\ln\ln n\right).
Reconstruction of graph colourings
A -deck of a (coloured) graph is a multiset of its induced -vertex
subgraphs. Given a graph , when is it possible to reconstruct with high
probability a uniformly random colouring of its vertices in colours from
its -deck? In this paper, we study this question for grids and random
graphs. Reconstruction of random colourings of -dimensional -grids from
the deck of their -subgrids is one of the most studied colour reconstruction
questions. The 1-dimensional case is motivated by the problem of reconstructing
DNA sequences from their `shotgunned' stretches. It was comprehensively studied
and the above reconstruction question was completely answered in the '90s. In
this paper, we get a very precise answer for higher . For every
and every , we present an almost linear algorithm that reconstructs
with high probability a random -colouring of vertices of a -dimensional
-grid from the deck of all its -subgrids for every and prove that the random -colouring is not
reconstructible with high probability if .
This answers the question of Narayanan and Yap (that was asked for )
on "two-point concentration" of the minimum so that -subgrids determine
the entire colouring. Next, we prove that with high probability a uniformly
random -colouring of vertices of a uniformly random graph is
reconstructible from its full -deck if and is not
reconstructible with high probability if . We further
show that the colour reconstruction algorithm for random graphs can be modified
and used for graph reconstruction: we prove that with high probability
is reconstructible from its full -deck if
while it is not reconstructible with high probability if
Safety of Spacecraft Participants Aboard Suborbital Reusable Launch Vehicles - Background Research
This presentation is an overview of commercial space safety regulatory environment and implications for government-sponsored spaceflight participants on commercial suborbital reusable launch vehicles
Safety of Spaceflight Participants Aboard Suborbital Reusable Launch Vehicles
The anticipated advent of the U.S. Government sponsoring human-tended research on commercial suborbital flights necessitates the establishment of safety review procedures for federal agencies to allow government-sponsored spaceflight participants (SFPs) aboard these vehicles. Safety practices for National Aeronautics & Space Administration (NASA) personnel aboard aircraft, orbital rockets and platforms, and a non- NASA vehicle, the Soyuz, are summarized. The valuable Recommended Practices for Human Space Flight Occupant Safety, published by the FAA Office of Commercial Space Transportation (FAA-AST) in 2014, are summarized. Medical recommendations for operationally critical flight crewmembers, published by the Aerospace Medical Association Commercial Spaceflight Working Group, are reviewed. FAA-AST approved SFP training available at three U.S. commercial companies is summarized. Activities of ASTM International Committee F47 on Commercial Spaceflight, formed in 2016, are reviewed. Finally, safety comparisons are made with another challenging environment, deep sea submersibles
Spectro-temporal shaping of seeded free-electron laser pulses
We demonstrate the ability to control and shape the spectro-temporal content
of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser
(FEL). The control over the spectro-temporal properties of XUV light was
achieved by precisely manipulating the linear frequency chirp of the seed
laser. Our results agree with existing theory, which allows retrieving the
temporal properties (amplitude and phase) of the FEL pulse from measurements of
the spectra as a function of the FEL operating parameters. Furthermore, we show
the first direct evidence of the full temporal coherence of FEL light and
generate Fourier limited pulses by fine-tuning the FEL temporal phase. The
possibility to tailor the spectro-temporal content of intense short-wavelength
pulses represents the first step towards efficient nonlinear optics in the XUV
to X-ray spectral region and will enable precise manipulation of core-electron
excitations using the methods of coherent quantum control.Comment: 5 pages, 3 figure
Synchronization of coupled stochastic limit cycle oscillators
For a class of coupled limit cycle oscillators, we give a condition on a
linear coupling operator that is necessary and sufficient for exponential
stability of the synchronous solution. We show that with certain modifications
our method of analysis applies to networks with partial, time-dependent, and
nonlinear coupling schemes, as well as to ensembles of local systems with
nonperiodic attractors. We also study robustness of synchrony to noise. To this
end, we analytically estimate the degree of coherence of the network
oscillations in the presence of noise. Our estimate of coherence highlights the
main ingredients of stochastic stability of the synchronous regime. In
particular, it quantifies the contribution of the network topology. The
estimate of coherence for the randomly perturbed network can be used as means
for analytic inference of degree of stability of the synchronous solution of
the unperturbed deterministic network. Furthermore, we show that in large
networks, the effects of noise on the dynamics of each oscillator can be
effectively controlled by varying the strength of coupling, which provides a
powerful mechanism of denoising. This suggests that the organization of
oscillators in a coupled network may play an important role in maintaining
robust oscillations in random environment. The analysis is complemented with
the results of numerical simulations of a neuronal network.
PACS: 05.45.Xt, 05.40.Ca
Keywords: synchronization, coupled oscillators, denoising, robustness to
noise, compartmental modelComment: major revisions; two new section
3D-Simulation of electromagnetic and temperature fields in the continuous induction heaters
The quasi-3-D model was developed for continuous induction heating of billets
with arbitrary cross section. This computer model is intended for evaluation of electrical and
thermal both stationary and non-stationary processes of stage and continuous working regime
an induction heater with magnetic and non-magnetic loading with any of cross section shape.
The combination of the most effective numerical methods for modeling induction heating
process was used in this software: Finite Difference Method (FDM), Finite Element Method
(FEM), Boundary Element Method (BEM), Integral Equation Method (IEM) and their
combination
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